混凝土介观热-湿-力耦合离散模型与高温爆裂机理研究

Concrete tends to be sensitive to explosive spalling due to the combined effect of thermal stress and pore vapor pressure, when it is exposed to fire. Its sensitivity to the thermal spalling can degrade the bearing capacity of concrete structure, and then induce structure failure. The key to scientifically preventing concrete thermal spalling is to understand the mechanism in this phenomenon. In the present literature, most multi-physics coupled models are based on continuous medium theory. These models are generally unable to describe the discrete process of thermal spalling, leading to the indetermination of the most important factor in thermal spalling so far. In order to overcome the inability of these continuous medium models, a discrete hygro-thermo-mechanical coupling model within the framework of the Lattice Discrete Particle Model (LDPM) will be proposed in this project, and then the thermal spalling mechanism will be studied by using this discrete model. The main contents are listed as follows. (a) The coupling mechanisms on hygro-mechanical, thermo-mechanical and thermo-hygro of concrete at high temperature will be studied and then the corresponding discrete numerical methods can be formulated, respectively; (b) A discrete mesoscale thermo-hygro-mechanical coupling model of concrete at high temperature within the framework of LDPM will be proposed; (c) The proposed model will be validated by the experiments carried out in this project. The proposed and validated model is expected to be able to mimic the behavior of concrete at high temperature and to gain a deep understanding on the spalling mechanism from the angle of energy transportation and transformation during the thermo-hygro-mechanical coupling process. These achievements would become the science basis for the enhancing of concrete fire resistance and the prevention of thermal spalling.

火灾高温下混凝土受温度应力和孔隙蒸气压力共同作用易发生爆裂破坏，降低混凝土结构承载能力，甚至引发结构系统性破坏。预防混凝土高温爆裂的科学核心是揭示高温爆裂机理。该方面现有研究多基于均匀连续介质模型展开，难以刻画爆裂引发的离散行为，致使高温爆裂主导因素尚不明晰。据此，项目为克服连续介质模型的局限性，采用混凝土介观非均质离散模型，开展混凝土高温热-湿-力耦合模型与爆裂机理研究，主要研究：分别揭示高温条件下混凝土热-力、热-湿、湿-力耦合机制，并基于介观离散模型提出各耦合环节的模拟方法；综合考虑热、湿、力耦合作用，建立混凝土介观高温热-湿-力耦合离散模型；开展混凝土高温爆裂物理实验检验所提模型，随后开展数值分析揭示爆裂主导因素。项目有望建立精细刻画高温作用下混凝土行为的数值方法，从热-湿-力耦合过程能量分配的角度阐明混凝土高温爆裂机理，为增强混凝土抗火能力及预防高温爆裂提供科学依据。

火灾高温下混凝土受温度应力和孔隙蒸气压力共同作用易发生爆裂破坏，降低混凝土结构承载能力，甚至引发结构系统性破坏。预防混凝土高温爆裂的科学核心是揭示高温爆裂机理。项目克服连续介质模型的局限性，构建以离散力学本构为基础的双重格构拓扑，建立混凝土介观热-湿-力耦合离散模型。所提模型能够精细描述混凝土内部水分迁移行为，并且是首个能够近真实刻画混凝土高温爆裂动态过程的数值模型。利用所提模型，成功破解困扰领域40年的混凝土高温爆裂机理问题，发现温度应力是混凝土高温爆裂的主导机理即主要能量来源，而孔隙蒸气压力学说则是次要机理也是出发因素。同时，论证地质雷达技术探测结构内水分迁移行为的可行性，为混凝土结构内干湿界面无损监测提供新方法。